A, The location of the needles for the sham–percutaneous
electrical nerve stimulation (PENS) and PENS treatments. With PENS
therapy, each of the 5 bipolar electrical stimulating leads are
connected to a pair of needles, alternating the positive and negative
positions. B, The location of the 4 cutaneous electrode pads used
during the transcutaneous electrical nerve stimulation (TENS)
treatments.

Change in the daily oral intake of nonopioid analgesic medications
during the 3-week treatment period with each of the 4 study modalities.
Values are mean (SEM). Asterisk indicates value is significantly
different from prestudy value (P<.008) and from
sham–percutaneous electrical nerve stimulation (PENS), transcutaneous
electrical nerve stimulation (TENS), and exercise therapy values
(P<.03). Dagger indicates value is significantly different
from prestudy value (P<.04).

Table 1. Comparison of the Average Visual Analog Scale Scores for Low Back Pain, Level of Activity, and Quality of Sleep Prior to Receiving the First Treatment and at 24 Hours After the Ninth Treatment With Each of the 4 Modalities*

Context Low back pain (LBP) contributes to considerable
disability and lost wages in the United States. Commonly used opioid
and nonopioid analgesic drugs produce adverse effects and are of
limited long-term benefit in the management of this patient population.

Results PENS was significantly more effective in decreasing
VAS pain scores after each treatment than sham-PENS, TENS, and exercise
therapies (after-treatment mean ± SD VAS for pain, 3.4 ± 1.4 cm, 5.5
± 1.9 cm, 5.6 ± 1.9 cm, and 6.4 ± 1.9 cm, respectively). The average
± SD daily oral intake of nonopioid analgesics
(2.6±1.4 pills per day) was decreased to
1.3±1.0 pills per day with PENS (P<.008)
compared with 2.5±1.1, 2.2±1.0, and
2.6±1.2 pills per day with sham-PENS, TENS, and
exercise, respectively. Compared with the other 3 modalities, 91% of
the patients reported that PENS was the most effective in decreasing
their LBP. The PENS therapy was also significantly more effective in
improving physical activity, quality of sleep, and sense of well-being
(P<.05 for each). The SF-36 survey confirmed that PENS
improved posttreatment function more than sham-PENS, TENS, and
exercise.

Conclusions In this sham-controlled study, PENS was more effective
than TENS or exercise therapy in providing short-term pain relief and
improved physical function in patients with long-term LBP.

Despite the
fact that low back pain (LBP) is one of the most common medical
problems in our society,1 current analgesic therapies
remain largely unsatisfactory. Conservative treatment with
anti-inflammatory drugs and exercise is effective for many patients
with acute LBP.2 However, when the pain symptoms persist,
they can interfere with both physical activity and sleep patterns.
While analgesic medications can provide temporary pain relief, these
drugs may not improve physical function and are associated with
well-known adverse effects. Interest in nonpharmacologic alternatives
has led to evaluations of transcutaneous electrical nerve stimulation
(TENS),3 acupuncture,4,5
electroacupuncture,6 spine manipulation,7- 9 and
exercise therapy9- 12 in the management of LBP. However,
controversy exists regarding the relative efficacy of these
nonpharmacologic therapies in the management of LBP because most of the
published studies lacked appropriate control (sham) groups or failed to
include relevant comparators.

Percutaneous electrical nerve stimulation (PENS) is a novel analgesic
therapy13 that combines the advantages of both TENS and
electroacupuncture by using acupuncturelike needle probes positioned in
the soft tissues and/or muscles to stimulate peripheral sensory nerves
at the dermatomal levels corresponding to the local pathology. In a
preliminary study,14 PENS therapy was found to be
preferable to TENS and relaxation therapies in the management of pain
secondary to osteoarthritis. Therefore, we designed a prospective,
randomized, sham-controlled, crossover trial to compare PENS with TENS
and exercise therapy in patients with long-term LBP secondary to
degenerative disk disease. In addition to assessing the pain response,
the patients' physical activity, quality of sleep, sense of
well-being, and oral analgesic requirements were evaluated.

METHODS

After obtaining institutional review board approval and
written informed consent, 60 patients (29 men and 31 women; mean ± SD
age, 43±1.9 years, and weight, 66±1.6
kg) with LBP secondary to radiologically confirmed degenerative disk
disease were administered 4 different nonpharmacologic treatment
modalities according to a randomized, sham-controlled, crossover study
design. The 4 modalities consisted of sham-PENS, PENS, TENS, and
flexion-extension exercise. Inclusion criteria included age older than
18 years, absence of any acute or long-term illnesses involving major
organ systems, and a history of LBP, which had been maintained at a
stable level with oral nonopioid analgesics for at least 3 months prior
to enrollment in the study. Exclusion criteria included a history of
drug or alcohol abuse, long-term use of opioid-containing medication, a
change in the character or severity of the pain within the last 3
months, presence of acute nerve root irritation (sciatica), previous
use of nontraditional analgesic therapies (eg, acupuncture), pending
medicolegal litigation (or worker's compensation claim), or an
inability to complete the health status assessment questionnaires.
Patients were told that we were comparing 4 different nonpharmacologic
therapies for LBP.

All patients received the 4 treatment modalities
according to 1 of 4 different computer-generated sequences: (1) PENS,
sham, TENS, and exercise; (2) sham, TENS, exercise, and PENS; (3) TENS,
exercise, PENS, and sham; or (4) exercise, PENS, sham, and TENS. Each
treatment was administered for 30 minutes 3 times a week (on Monday,
Wednesday, and Friday afternoons) for 3 weeks. Upon completion of each
3-week treatment block, the patient was given 1 week off before
starting the next modality. The 4 modalities were administered to all
patients over the 15-week study period.

Treatment Modalities

The basic PENS therapy consisted of the placement of ten 32-gauge
stainless steel acupuncturelike needle probes into the soft tissue
and/or muscle in the lower back region to a 2- to 4-cm depth according
to the dermatomal distribution of the pain as illustrated in part A of
Figure 1. The probes were connected
to 5 bipolar leads (with each lead connected to 1 positive and 1
negative probe) from an investigational (not approved by the Food and
Drug Administration) low-output (<25 mA) electrical generator, which
produced a unipolar square-wave pattern of electrical stimulation at a
frequency of 4 Hz with a pulse width of 0.5 milliseconds. The intensity
of the electrical stimulation was adjusted to produce the maximum
tolerable "tapping" sensation without muscle contractions.

The sham-PENS therapy consisted of the placement of 10 acupuncturelike
needle probes in an identical montage (Figure 1, A); however, no
electrical stimulation was applied to the probes.

The TENS therapy consisted of the placement of 4 medium-sized (2.5-cm)
cutaneous electrode pads (SnapEase, Empi, St Paul, Minn) in a standard
dermatomal pattern (Figure 1, B). These electrodes were also stimulated
at a frequency of 4 Hz, with a pulse duration of 0.1 milliseconds.

The lower back exercise therapy consisted of spine flexion and
extension with
the patient seated on a chair with full abduction
of both hips.15 The patient was instructed to slowly touch
the floor with both hands while remaining seated, followed by full
extension of the back. This maneuver was repeated a minimum of 30 times
during each 30-minute treatment session.

Assessment Procedures

Prior to initiating the first of the 4 treatments, patients were
required to complete the Health Status Survey Short Form
(SF-36).16 The physical component summary (PCS) and mental
component summary (MCS) scores were used to assess the patient's
response to each of the therapeutic modalities.17 All
patients were also asked to assess their baseline level of LBP,
physical activity, and quality of sleep during the 48-hour interval
prior to each treatment session using standard 10-cm visual analog
scales (VASs), with a score of zero equalling the best to a score of 10
equalling the worst (Table 1). Repeated VAS assessments of pain, activity, and sleep were performed 3
times a week prior to each treatment session by the patient. In
addition, the pain VAS was repeated immediately after completion of
each treatment. The SF-36 was repeated 24 hours after completing all 9
treatment sessions with each of the 4 modalities. Patients were
instructed not to change the type of nonopioid analgesic medications
used during the course of the study. They were also asked to maintain a
diary in which they recorded their daily usage of all analgesic
medications (eg, pills per day) and any unusual reactions to the
investigational therapies. Finally, each patient completed an overall
assessment of the relative effectiveness of the 4 different modalities
72 hours after the last treatment session.

Data Analysis

The Number Cruncher Statistical System software program (version 6.0.1
for Windows, Kaysville, Utah) was used for all statistical analyses. An
a priori power analysis (α, .05; β, .10; power, 90%; and SD, 2.0)
determined that a group size of 60 should be adequate to demonstrate a
difference of 25% between the VAS scores for the 4 modalities. The
changes in the VAS scores over time were analyzed with repeated
measures analysis of variance and t test, with a Bonferroni
comparison test (vs control values and pairwise data), applied for
multiple comparisons. Analysis of discrete (noncontinuous) data for the
4 treatment modalities was performed using the χ2 test.
The pretreatment and posttreatment changes and the differences between
the modalities in the SF-36 scores were analyzed by paired t
tests.

RESULTS

The pretreatment SF-36 evaluation suggested that this LBP population
reported significantly lower health-related quality-of-life scores
compared with the general population. The prestudy scores for this LBP
population were 28.4±8.4 and 40.2±5.0
for the PCS and MCS, respectively, compared with general population
norms of 50 for these 2 summary scores.18 The post-PENS
treatment SF-36 scores were significantly improved over the prestudy
scores for both the PCS (34.2±7.4;
P=.003) and MCS (42.8±5.2;
P = .007) components. Both TENS and sham-PENS produced small
but statistically significant improvements in the PCS
(29.6±8.4 and 29.4±8.6, respectively)
and MCS (41.1±5.5 and 41.0±5.4,
respectively) scores (P<.02). When the changes in the SF-36
scores with the PENS therapy were compared with the other 3 modalities,
PENS was found to produce significantly greater improvement in
posttherapy function (eg, PENS vs sham-PENS differences were
+4.97±2.99 and +1.84±3.56 for PCS and
MCS, respectively; PENS vs TENS differences were
+4.66±2.85 and +1.7±4.19 for PSC and
MCS, respectively; and PENS vs exercise differences were
+5.82±2.93 and +1.84±3.56 for PCS and
MSC, respectively).

The VAS scores for pain, physical activity, and quality of sleep prior
to the first treatment session (baseline) and 24 hours after the last
treatment session with each of the 4 modalities are summarized in
Table
1. Compared with the baseline values, posttreatment VAS scores for
pain, physical activity, and quality of sleep were improved by
46%±18%, 42%±19%, and
44%±20%, respectively, with PENS therapy
(P<.007). TENS also produced significant decreases in the
degree of pain and improvement in physical activity after 6 of 9
treatment sessions (P<.03) with an average overall
improvement in the degree of pain and physical activity (from the
baseline values) of 11%±14% and
15%±16%, respectively. No significant pain-relieving
effects were demonstrated with either the sham-PENS or exercise
therapies. Comparing the effects of the 4 treatment modalities on VAS
scores for pain, physical activity, and sleep quality revealed that
PENS produced significantly greater
improvements than sham-PENS, TENS, or exercise therapies
(P<.02).

PENS produced an acute analgesic effect immediately after each
treatment session (with an average 82%±23% decrease
in the pain VAS scores vs 26%±19%,
9%±15%, and 4%±11% decreases with
TENS, sham-PENS, and exercise, respectively). After 3 to 4 treatments
with PENS, patients began reporting significant improvement in their
pretreatment VAS scores for pain, activity, and sleep compared with
their baseline values (Figure 2). PENS also significantly decreased the consumption of oral
nonopioid analgesic medication
(P<.009) (Figure 3). Compared with the prestudy values, PENS therapy was associated with a
50% reduction in the daily oral analgesic requirement. In contrast,
TENS therapy decreased the need for analgesic medication on only 6 days
during the 3-week study period (P<.04). Neither sham-PENS
nor exercise therapies altered the patients' usage of their oral
analgesic medication.

Finally, the overall evaluation of the 4 treatment modalities indicated
that PENS was the preferred therapy in 91% of the study patients (Table 2). In addition, PENS was
reportedly more effective than TENS and exercise therapies in improving
the patients' physical activity and sense of well-being. More than
80% of the patients indicated that they would be willing to pay extra
money (out-of-pocket) to receive PENS therapy in the future.

COMMENT

This crossover, sham-controlled study demonstrated that PENS was more
effective than TENS and exercise therapies in providing short-term
relief of pain and in improving function in patients with stable LBP of
at least 3 months' duration. PENS was also significantly more
effective than TENS and exercise therapies in reducing the need for
oral analgesic medications. These findings are consistent with earlier
studies by Deyo et al19 and Marchand et al,20
suggesting that TENS therapy is only marginally more effective than a
placebo treatment (eg, sham-PENS) in this patient population. Of
interest, Moore and Shurman21 reported that combined
neuromuscular electrical stimulation with TENS was significantly more
effective than TENS alone in the management of long-term back pain.

PENS therapy was also highly effective in producing acute
analgesia in this LBP population. More importantly, the patients began
to report more sustained beneficial effects on their level of pain and
physical activity, as well as their quality of sleep, after 3 to 4 PENS
treatments. Due to the apparent cumulative effects of PENS over the
course of the 3-week treatment period, these data would suggest that
the use of this treatment modality over a longer period of time has the
potential to produce prolonged beneficial effects in patients with
long-term LBP. However, a more prolonged period of PENS therapy with
careful follow-up at 3-, 6-, and 12-month intervals would be required
to assess the long-term effects of this novel therapeutic modality in
improving patient outcome.

Enhanced physical activity may be the most important outcome
variable in the treatment of LBP.19,22,23 To achieve the
maximal benefit from nonpharmacologic (so-called complementary)
analgesic therapies such as PENS, it is recommended that PENS be used
as part of a multimodality rehabilitation program, which also includes
an ongoing exercise program. Although the simple spine
flexion-extension exercise used in this investigation failed to produce
a significant improvement in patient well-being when administered
alone, this may be a reflection of the lack of effectiveness of this
particular exercise maneuver or an inadequate period of exercising. In
contrast to our findings, other investigators have found a more
extensive exercise program to be as effective as TENS in reducing pain
scores and disability in workers with acute LBP.24 Future
studies need to evaluate the effectiveness of PENS therapy in
combination with a comprehensive exercise program.

The results of the SF-36 psychological assessments further
support and strengthen the clinical findings by providing additional
outcome measures, which demonstrates the superiority of PENS over the
other
nonpharmacologic treatments used in
this study. These data suggest that PENS therapy was the most
beneficial modality in improving the physical (eg, fewer limitations in
self-care, less severe body pain) and mental (eg, less psychological
distress, less disability due to emotional problems) health and
well-being of these patients with long-term LBP.

The nature of the electrical (tapping) sensations precluded our
ability to perform the treatments in a double-blind fashion. In an
attempt to minimize investigator bias, all patient assessments were
performed by individuals not involved in administering the therapies.
To avoid prejudicing patients in favor of PENS therapy, the sham
treatment was described to the patients as an acupuncturelike therapy.
Since the needles for the sham-PENS treatments were placed in a
dermatomal montage rather than at specific acupoints, it would be
inappropriate to conclude that classic Chinese acupuncture is of no
benefit in this patient population.

Another potential criticism of the study design relates to the
selection of a low-stimulus frequency (4 Hz) for 30-minute intervals
for both the PENS and TENS treatments. However, Walsh et
al25 reported that the hypoalgesic effect of TENS was more
effective at 4 Hz than 110 Hz. Other investigators have found that more
prolonged periods of stimulation (>40 minutes) may be associated with
the development of tolerance to the analgesic effect of the electrical
stimulus.26

Future studies are clearly needed to determine the relative
effectiveness of different frequencies and durations of electrical
stimulation with PENS therapy. Preliminary experience with PENS in
other patient populations suggests that an improved analgesic response
may be achieved by using higher (50-100 Hz) or mixed (15 Hz and 30 Hz)
stimulating frequencies at subsequent treatment
sessions.13,14 Similarly, this dermatomal montage was
selected as a starting point for PENS therapy because it was found to
be highly effective in this patient population during our pilot
studies. However, depending on the associated manifestations of the
pain (eg, radiation down the leg), other needle locations may prove to
be more effective for subsequent PENS treatments.

Since long-term LBP is extremely costly to society and can have
debilitating effects on both patients and their families, this patient
population is increasingly turning to unconventional alternative
medical practices (including various forms of nonpharmacologic
analgesic therapies).27 In determining the cost benefit of
any new analgesic therapy, it is important to carefully consider both
the pertinent costs (eg, equipment, disposables, personnel
requirements) and the consequences or outcome of the treatment (eg,
patient satisfaction, quality of life, resumption of normal activities)
in monetary terms.28 Future studies should be designed to
examine the cost benefit of using PENS therapy as part of a multimodal
approach, which would also include anti-inflammatory analgesic drugs
and a low back exercise program.

In conclusion, this sham-controlled study demonstrated that PENS
is more effective in improving short-term outcomes than TENS and
exercise therapies in patients with long-term LBP. The use of PENS
therapy significantly decreased the need for oral nonopioid analgesic
medications in this patient population.